[PATCH v2] KVM: arm64: PMU: Restore the guest's EL0 event counting after migration

[Reiji Watanabe <reijiw@google.com>]

Currently, with VHE, KVM enables the EL0 event counting for the
guest on vcpu_load() or KVM enables it as a part of the PMU
register emulation process, when needed.  However, in the migration
case (with VHE), the same handling is lacking, as vPMU register
values that were restored by userspace haven't been propagated yet
(the PMU events haven't been created) at the vcpu load-time on the
first KVM_RUN (kvm_vcpu_pmu_restore_guest() called from vcpu_load()
on the first KVM_RUN won't do anything as events_{guest,host} of
kvm_pmu_events are still zero).

So, with VHE, enable the guest's EL0 event counting on the first
KVM_RUN (after the migration) when needed.  More specifically,
have kvm_pmu_handle_pmcr() call kvm_vcpu_pmu_restore_guest()
so that kvm_pmu_handle_pmcr() on the first KVM_RUN can take
care of it.

Fixes: d0c94c49792c ("KVM: arm64: Restore PMU configuration on first run")
Cc: stable@vger.kernel.org
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Reiji Watanabe <reijiw@google.com>

---
v2:
 - Added more explanation to the commit message [Marc]
 - Added Marc's r-b tag (Thank you!)

v1: https://lore.kernel.org/all/20230328034725.2051499-1-reijiw@google.com/
---
 arch/arm64/kvm/pmu-emul.c | 1 +
 arch/arm64/kvm/sys_regs.c | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 24908400e190..74e0d2b153b5 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -557,6 +557,7 @@ void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
 		for_each_set_bit(i, &mask, 32)
 			kvm_pmu_set_pmc_value(kvm_vcpu_idx_to_pmc(vcpu, i), 0, true);
 	}
+	kvm_vcpu_pmu_restore_guest(vcpu);
 }
 
 static bool kvm_pmu_counter_is_enabled(struct kvm_pmc *pmc)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 53749d3a0996..425e1e9adae7 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -794,7 +794,6 @@ static bool access_pmcr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 		if (!kvm_supports_32bit_el0())
 			val |= ARMV8_PMU_PMCR_LC;
 		kvm_pmu_handle_pmcr(vcpu, val);
-		kvm_vcpu_pmu_restore_guest(vcpu);
 	} else {
 		/* PMCR.P & PMCR.C are RAZ */
 		val = __vcpu_sys_reg(vcpu, PMCR_EL0)

base-commit: 197b6b60ae7bc51dd0814953c562833143b292aa
-- 
2.40.0.348.gf938b09366-goog